1. Field of the Invention
The present invention relates generally to medical diagnostic procedures. More particularly the invention relates to use of a kinematic imaging table for rapid positional changes in patients"" centering for use with a magnetic resonance imaging (MRI) machine. The kinematic imaging table is constructed of a non-magnetic material, so as not to interfere with the magnetic resonance imaging and may be motorized to allow automatic positional changes in patient centering under computer control during the diagnostic procedures. The diagnostic procedure entails the use of this table or other means to effect rapid positional changes, injection of an MRI contrast agent and the use of rapid imaging MRI sequences for the display of vascular territories along different anatomical positions of the body. According to another aspect of the present invention, a patient is injected with a contrast material, and multiple images are taken at different overlapping orientations using a single injection of an MRI contrast agent.
2. Background and Summary of the Invention
Various magnetic resonance angiography (MRA) techniques have been routinely employed in the past for imaging both arteries and veins in the body. The predominant techniques employed on a routine basis in clinical practice include 2D and 3D-time of flight (TOF), phase contrast and contrast-enhanced techniques. These techniques all have their advantages and are routinely employed to image specific target areas within the body. When imaging multiple target sites, however, all these techniques have their own inherent limitations. The clinical need for imaging multiple anatomic areas in the body is frequently encountered in practice, especially when evaluating the aorta. Patients with aortic dissection, require imaging of the thoracic and abdominal aorta. As such, two anatomical locations, specifically the chest and abdomen, need to be imaged. Patients with abdominal aortic disease and disease of the lower extremity arteries, require imaging of the abdomen, pelvis, thighs and legs down to and including the ankle region.
In conventional clinical practice, these territories are imaged with x-ray angiography following injection of iodinated contrast material directly into the aorta. Direct injection is via catheters that are placed within the aorta following arterial puncture and percutaneous placement of catheters, typically from the groin. These invasive techniques have a number of complications that are related not only to arterial puncture but also to the iodinated contrast that is administered. Complications such as thrombosis and occlusion of the femoral artery, pseudoaneurysm formation, bleeding and peripheral emboli are a few of the non-contrast related complications. Iodinated contrast complications include allergic reactions ranging from minor skin reactions to anaphylactic shock and death, and renal failure from contrast induced nephrotoxicity.
It is for these reasons, that MRI machines have been employed to image the arteries and veins using MRA techniques. 2D-time-of-flight techniques have been used to study the aorta and run-off circulation, however, even with the current state-of-the-art technology, multiple transverse slices are required with typical table times of 1.5 to 2 hours required for a complete examination covering the abdominal aorta to the ankle region. These techniques do not use intravenous contrast and image the blood vessels due to the inherent contrast of moving blood on gradient echo sequences due to the flow related enhancement phenomenon. Phase contrast techniques are likewise, time consuming. As such, breath-hold contrast enhanced techniques have been published in the literature, however, these have only been used in studying one anatomic region.
Currently, the FDA approved MRI contrast agents include gadopentetate dimeglumine (Magnevist, Berlex, Chicago, Ill.), gadoteridol (ProHance, Bracco Diagnostics, Princeton, N.J.) and gadodiamide (Omniscan, Nycomed). The first of these agents is an xe2x80x9cionicxe2x80x9d agent and the latter of these two agents are xe2x80x9cnon-ionicxe2x80x9d or net-0 charge agents with lower osmolality. The lower osmolality agents are approved for higher dose administrations. All of these agents are classified as extracellular agents that extravasate from the blood pool into the extracellular fluid space in a rapid manner. Pharmacokinetics have shown that 50% of the contrast dose that is injected into the peripheral vein of the upper extremity is cleared on first pass through the capillaries and 80% is cleared within five minutes. The route of elimination is via glomerular filtration through the kidneys. As such, rapid techniques are required to image the target arteries once the contrast is injected into the upper extremity vein. Likewise, one needs to appropriately time the data acquisition when the contrast arrives at the target site. Once the target site has been imaged, the data is processed yielding high resolution imaging of both arteries and veins. Veins are imaged by acquiring a delayed acquisition when venous return leads to the enhancement of the veins. Data subtraction of the arterial phase and venous phase data is performed to yield vein only images. The limitations of contrast-enhanced techniques for evaluating multiple anatomical locations, therefore, are primarily related to the current inability of any of the MRI machines available on the market in rapidly moving the patient table to image successive anatomical locations.
The details of an imaging table incorporating the use of surface coils is disclosed in our copending U.S. patent application, Ser. No. 08/766,289, entitled xe2x80x9cUniversal Kinematic Imaging Table for Rapid Positional Changes in Patient Centering,xe2x80x9d the disclosure of which is hereby incorporated by reference and summarized in the Detailed Description of the Preferred Embodiment presented below.
Therefore, it is desirable in the art of radiology to provide an imaging device which provides high resolution images and which permits rapid positional changes in patient centering so that the time required for obtaining accurate images of a patient may be reduced and so that movement of the patient relative to the imaging coils is simplified.
Accordingly, the present invention provides a magnetic resonance imaging device including an examination table movably supported on a track. A lower surface coil is supported under the table, and an upper surface coil is supported above the table. The table is movable relative to the upper and lower surface coils.
The present invention provides a procedure and apparatus which allows rapid positional change in the patient centering in order to facilitate the imaging of blood vessels in a series of different views, and to reduce the time required for obtaining the necessary images for a medical imaging examination using a single injection of an MRI contrast agent.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.